1. Field of the Invention
The present invention generally relates to rechargeable battery protection integrated circuit devices, rechargeable battery protection modules using the rechargeable battery protection integrated circuit devices, and battery packs. More specifically, the present invention relates to a rechargeable battery protection integrated circuit device including a short circuit detecting circuit, the short circuit detecting circuit being configured to convert a discharge current of a rechargeable battery to a voltage value and detect a short circuit state of the rechargeable battery when the voltage value is equal to or greater than a short circuit detecting voltage, a rechargeable battery protection module using the rechargeable battery protection integrated circuit device, and a battery pack.
2. Description of the Related Art
Conventionally, a rechargeable battery protection module configured to protect a rechargeable battery such as a lithium battery has been suggested. FIG. 1 is a circuit diagram of a related art rechargeable battery protection module 250 including a rechargeable battery protection integrated circuit 120. As shown in FIG. 1, the related art rechargeable battery protection module 250 is connected in parallel with a rechargeable battery and a charger is connected to terminals P+ and P− so that a battery pack 300 is formed. In the rechargeable battery protection module 250, as charge and discharge control FETs (Field Effect Transistor), N channel MOS (Metal Oxide Semiconductor) transistors M1 and M2 having 10 mΩ of on-resistance values are used. A charge and discharge electric current is converted to a voltage by the on-resistance values of the charge control MOS transistor M1 and the discharge control MOS transistor M2, so as to be detected by a V-terminal. On and off control of the charge control MOS transistor M1 is performed by a COUT terminal. The charge control MOS transistor M1 is turned off in an overcharge state or an abnormal charger connecting state (charge over-current state) so that the rechargeable battery is protected. In addition, on and off control of the discharge control MOS transistor M2 is performed by a DOUT terminal. The discharge control MOS transistor M2 is turned off in an over-discharge state, a discharge over-current state, or an output short-circuit state so that the rechargeable battery is protected.
The over-charge state and over-discharge state are detected by an overcharge detecting circuit 10 and an over-discharge detecting circuit 20 by monitoring a voltage of a VDD terminal. On the other hand, the charge over-current state, the discharge over-current state, and the output short-circuit state are detected by a charge over-current detecting circuit 40, a discharge over-current detecting circuit 30, and a short-circuit detecting circuit 50, respectively, by monitoring a voltage of the V-terminal.
The discharge of the rechargeable battery protection module 250 can be made via a body diode D1 of the charge control MOS transistor M1 even if the charge control MOS transistor M1 is turned off. The charging of the rechargeable battery protection module 250 can be made via a body diode D2 of the discharge control MOS transistor M2 even if the discharge control MOS transistor M2 is turned off. Accordingly, if the battery is in the overcharge state, when a load is connected, the battery is discharged so as to recover from the overcharge state. In addition, if the battery is in the over-discharge state, when a charger is connected, the rechargeable battery is charged so as to recover from the over-discharge state.
FIG. 2 is a view showing an example of a cross-sectional structure of a normal N channel MOS transistor, the transistor being applied to the charge control MOS transistor M1 and the discharge control MOS transistor M2. Referring to FIG. 2, a channel between a drain D and a source S is not opened if a positive voltage is not applied to a gate G. However, a forward current flows by a parasitic diode D1 of a PN junction via a P-type substrate, between the drain D and a back gate BG where the source S is connected. In other words, the electric current flows from the back gate BG (source S) to the drain D even if the N channel MOS transistor per se is turned off. In this case, a voltage generated in the PN junction when the forward current flows in the PN junction is 0.6 V through 0.7 V.
Referring back to FIG. 1, as discussed above with reference to FIG. 2, even if the charge control MOS transistor M1 is turned off, when the load is connected to the rechargeable battery, the discharge electric current flows in the forward direction of the body diode D1 and a positive voltage Vf (≈0.6 V) is applied to the charge control MOS transistor M1. Similarly, even if the discharge control MOS transistor M2 is turned off, when the charger is connected to the P+ terminal and the P− terminal, the charging electric current flows in the forward direction of the body diode D2 and a negative voltage is applied to the discharge control MOS transistor M2. Because of this, the battery pack 300 can discharge in the overcharge state if the load is connected and can be charged in the over-discharge state if the charger is connected.
For example, Japanese Laid-Open Patent Application Publication No. 2007-49796 has suggested a semiconductor device for protecting a rechargeable battery at least from excessive discharge current due to over-discharge of the rechargeable battery, the semiconductor device including a first excessive discharge current detection circuit configured to detect first excess of a voltage at an externally or an internally provided electric current detection terminal exceeding a first voltage level, the electric current detection terminal converting a discharge current to a positive voltage with respect to ground potential; a second excessive discharge current detection circuit configured to detect a second excess of the absolute voltage at the electric current detection terminal exceeding a second voltage level higher than the first voltage level; a delay circuit configured to cause each of the first and second excessive discharge current detection circuits to delay its output by a predetermined delay time; and a delay reducing circuit configured to produce a delay time reducing signal for reducing the delay time at a predetermined ratio when a negative voltage lower than a predetermined negative voltage level or a positive voltage higher than a third voltage level is applied to the electric current detection terminal. With this arrangement, each signal output from the first and second excessive discharge current detection circuits is delayed by a certain delay time produced by the delay circuit. This delay time can be adjusted or reduced at a predetermined ratio based on the delay time reducing signal, which signal is generated when a prescribed condition is satisfied. This arrangement can deal with different levels of excessive discharge currents without increasing the area size of the IC chip.
In the meantime, the structure of the related art device shown in FIG. 1 has the following problems. In a case where the load is connected during the overcharge detecting of the rechargeable battery protection module 250 so that the rechargeable battery is discharged, when a voltage of the V-terminal is increased by Vf by the body diode D1 of the charge control MOS transistor M1 so that an increase of electric potential of the V-terminal by the body diode D1 becomes equal to or greater than a short-circuit detecting voltage, a short-circuit protection function works. In other words, in this case, if the discharge control MOS transistor M2 is turned off when the charge control MOS transistor M1 is turned off due to detection of an overcharge, both charge and discharge cannot be performed.
For example, when the short circuit detection voltage of the V-terminal is 0.5 V and on-resistance of the charge control MOS transistor M1 is 50 mΩ, the short circuit protection works in the case of a short circuit electric current being equal to or greater than 10 A. In this case, while setting of the short circuit electric current is proper, if the short circuit detecting voltage is 0.5 V, the voltage of the V-terminal is increased to approximately 0.6 V at the forward direction voltage Vf of the body diode D1 and thereby the short circuit protection function acts. As a result of this, regardless of the overcharge state, the discharge control MOS transistor M2 is turned off, so that both charge and discharge cannot be performed.
Because of this, as a measure to avoid such a condition, for example, the short circuit detection may not be performed in the overcharge state. However, with this measure, discharging can be performed in the overcharge state. Therefore, while it is possible to handle the battery pack 300, the rechargeable battery cannot be protected when the short circuit of the rechargeable pack 300 occurs during the overcharge state. Hence, there may be a serious problem with the protection function of the rechargeable battery.
As an alternative measure, the short circuit detection voltage may be greater than the amount of increase of the V-terminal by the forward direction voltage Vf of the body diode D1 of the charge control MOS transistor M1. In this case, while discharging in the overcharge state can be performed and protection against the load short circuit during the overcharge state can be provided, the short circuit detection threshold value at the normal time may be greater. In other words, if the short circuit detection threshold value is too high, the range where the short circuit protection works at the normal time may become narrow. For example, when the short circuit detection threshold value is 1.0 V higher than 0.6 V, in a case where the on-resistance of the charge control MOS transistor M1 is 50 mΩ, the short circuit protection is performed at the short circuit electric current equal to or greater than 20 A. However, this electric current is too large and it is necessary to perform the short circuit protection when smaller short circuit electric currents flow.
FIG. 3 is a circuit diagram showing a short circuit state of the related art battery pack 300. More specifically, in the example shown in FIG. 3, the short circuit of the battery pack 300 is made by the load of the impedance RL 130. As shown in FIG. 3, the short circuit of the battery pack 300 is made with the impedance RL of several 100 mΩ by a contact resistance, a broken line resistance, the fuse 140 for protecting the physical over-current, or the like. The short circuit electric current at this time is limited by an inside impedance of the rechargeable battery and the impedance RL 130. Accordingly, in a case where the electric current limitation by which the short circuit protection is operated is too large, the protection may not be provided when the protection is required.
In a small size and low consumption electric current device using a rechargeable battery having a large internal impedance and small output electric current capability, safe properties are increased by setting the short circuit detection voltage low. Accordingly, if the short circuit detection voltage of the rechargeable battery protection module 250 is set to be greater than the voltage increase Vf by the body diode D1 of the charge control MOS transistor M1, it may be difficult to meet the demands of the small size and low consumption electric current device.
In addition, in the above-mentioned structure suggested in Japanese Laid-Open Patent Application Publication No. 2007-49796, although several values of the discharge over-current are set and corresponding various delay times can be set, the delay time at the time of detection is merely changed based on the value of the detection voltage. Therefore, the problems of the short circuit detection at the time of overcharging being the same as those in the related art may remain.